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Proteins
– Monomer: Amino acids
– Polymer: Polypeptide (aka protein)
– Key Elements: C, H, N, “R” (R varies)
Proteins are:
a) Hydrophobic
b) Hydrophilic
c) Could be either
d) Not sure
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Protein Functions
• Proteins are >50% of the dry mass of most cells
– Structural support
– Storage
– Transport
– Cellular communications
– Movement
– Defense against foreign substances
– ALL enzymes are proteins – chemical reactions wouldn’t
occur in our cells without proteins!
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Functions of Proteins: Examples
Proteins have many diverse functions; they are the most
functionally diverse type of macromolecules
1. Structural support (e.g. silk of spider webs)
2. Storage of energy & nitrogen
(e.g. egg albumin)
3. Transport of substances within organisms
(e.g. hemoglobin) or across membranes
(e.g. aquaporins)
4. Signaling: long-distance (e.g. insulin) or
short-distance; gene-regulatory proteins;
receptor proteins
Functions of Proteins: Examples
Proteins have many diverse functions; they are the most
functionally diverse type of macromolecules
5. Defense against invading pathogens (e.g. antibodies in immune system)
Antibody protein
Protein from flu virus
6. Movement (e.g. muscle proteins)
ATP
Actin and
Myosin
7. Metabolic catalysts (enzymes)
Enzymes speed up chemical
reactions
Fig. 8.16
Essential amino acids
Fig. 41.2
Methionine
Valine
Beans
and other
legumes
Threonine
Phenylalanine
Leucine
Corn (maize)
and other grains
Isoleucine
Tryptophan
Lysine
So, a diet of only wheat bread and corn would not be sufficient.
Peptide bond is C-N bond
between neighboring amino
acids formed by removal of
H2O (dehydration synthesis).
Peptide
bond
Side chains
Peptide
bond
Since amino acids in proteins
are bonded together by
peptide bonds, proteins are
also called polypeptides.
Backbone
Fig. 5.18
Levels of protein structure
Primary
Structure
Secondary
Structure
Tertiary
Structure
Quaternary
Structure
 pleated sheet
Examples of
amino acid
subunits
 helix
Fig. 5.21
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Primary Structure
1
Exact sequence of amino
acids is called the primary
structure of a protein.
5
10
Amino acid
subunits
15
20
25
Fig. 5.21
Levels of protein structure
Primary
Structure
Secondary
Structure
 pleated sheet
Examples of
amino acid
subunits
 helix
Fig. 5.21
Tertiary
Structure
Quaternary
Structure
Secondary Structure
 pleated sheet
 helix
Fig. 5.21
Secondary structure:
Helix or pleated sheet.
Pleated sheet protein often used for structural purposes
Spider’s abdominal glands
secrete silk fibers made
of structural protein
with  pleated sheets.
Fig. 5.21
Levels of protein structure
Primary
Structure
Secondary
Structure
 pleated sheet
Examples of
amino acid
subunits
 helix
Fig. 5.21
Tertiary
Structure
Quaternary
Structure
Polypeptide
backbone
Tertiary structure
results from
various kinds of
interactions
between atoms of
the side chains
(R groups).
Fig. 5.21
Levels of protein structure
Primary
Structure
Secondary
Structure
 pleated sheet
Examples of
amino acid
subunits
 helix
Fig. 5.21
Tertiary
Structure
Quaternary
Structure
Polypeptide
chain
 Chains
Quarternary
structure is
the interaction
of different
subunits.
Iron
Heme
 Chains
Hemoglobin
Collagen
Fig. 5.21
Normal hemoglobin
Primary
structure
Val His Leu Thr Pro Glu Glu
1
2
3
4
5
7
6
Secondary
and tertiary
structures
 subunit


Quaternary Normal
hemoglobin
structure
(top view) 
Changes in primary
structure can have a
profound effect on
protein function.

Fig. 5.22
Function
Molecules do
not associate
with one
another; each
carries oxygen.
Fig. 5.22
Sickle-cell hemoglobin
Normal hemoglobin
Primary
structure
Val His Leu Thr Pro Glu Glu
1
2
3
4
5
7
6
Secondary
and tertiary
structures
Val His Leu Thr Pro Val Glu
Exposed 1
hydrophobic
region
2
Sickle-cell
hemoglobin

4
5
6
7
 subunit


Quaternary Normal
hemoglobin
structure

Function
3
Molecules do
Not stick
to each
other; each
carries oxygen



Molecules
crystallize
into fiber;
capacity
to carry
oxygen
greatly
reduced

Fig. 5.17
Amino acid R (rest) groups
Nonpolar R groups: hydrophobic
Glycine
Alanine
Valine
Electrically
Charged
R groups:
hydrophilic
Aspartic acid Glutamic acid
Lysine
Leucine
Arginine
Isoleucine
Histidine
Fig. 5.22
Sickle-cell hemoglobin
Normal hemoglobin
Primary
structure
Val His Leu Thr Pro Glu Glu
1
2
3
4
5
7
6
Secondary
and tertiary
structures
Val His Leu Thr Pro Val Glu
Exposed 1
hydrophobic
region
2
Sickle-cell
hemoglobin

4
5
6
7
 subunit


Quaternary Normal
hemoglobin
structure

Function
3
Molecules do
Not stick
to each
other; each
carries oxygen



Molecules
crystallize
into fiber;
capacity
to carry
oxygen
greatly
reduced

10 µm
Normal red blood
cells are full of
individual
hemoglobin
molecules, each
carrying oxygen.
10 µm
Fibers of abnormal
hemoglobin deform
red blood cells into
sickle shape.
Fig. 5.22
The Genetics of Sickle Cell Anemia
• Sickle cell anemia is a recessive disorder.
• AA (homozygous dominant) don’t have symptoms.
• aa (homozygous recessive) have severe symptoms,
including:
• Low body oxygen levels
• Severe pain
• Swelling of hands and feet
• Frequent infections (spleen)
• Delayed growth/development
• Vision problems
• What about heterozygotes (Aa)?
• Usually lack negative effects, but
high stress situations can trigger symptoms
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Why hasn’t natural selection eliminated sickle cell anemia?
Some clues:
• 1 in 10 African Americans is a carrier for sickle cell anemia
• Rates of sickle cell anemia are also higher in people with
Mediterranean, Middle Eastern, and Indian ancestry
“Heterozygote Advantage”
Fig. 23.17
Frequencies of the
sickle-cell allele
Distribution of
malaria caused by
Plasmodium falciparum
(a parasitic unicellular eukaryote)
0–2.5%
2.5–5.0%
5.0–7.5%
7.5–10.0%
10.0–12.5%
>12.5%
Sickle-cell disease inheritance.
http://en.wikipedia.org/wiki/Sickle-cell_disease
• Individuals with two copies of the altered gene suffer
many complications (pain, infections, stroke, etc.), but are
resistant to malaria.
•Individuals with one copy suffer few complications and
are also resistant.
Fig. 5.17
Amino acid R (rest) groups
Nonpolar R groups: hydrophobic
Glycine
Alanine
Valine
Electrically
Charged
R groups:
hydrophilic
Aspartic acid Glutamic acid
Lysine
Leucine
Arginine
Isoleucine
Histidine
Today’s Exit Ticket
The bonds creating the primary structure of a protein are
called 1)___________ and form between a 2)___ atom in
one amino acid and a 3)____ atom in another amino acid.
The bonds creating the secondary structure of a protein are
called 4)__________ and form between 5)___________.
The bonds creating the tertiary structure of a protein can be
covalent, ionic, or hydrogen bonds, and form between
6)_______________.
7) Describe the quaternary structure of a protein.